Pre-Lab oratory Assignment 1 Describe the safety precautions...

Pre-Lab oratory Assignment 1 Describe the safety precautions you must take when removing the flask from the boiling-water bath. 2 A student doing this experiment collected the following data: temperature of boiling water $99.7^\circ C$ volume of water pulled into the flask 30.0 ml temperature of water in ice-water bath $0.1^\circ C$ volume of flask 134.0 ml. barometric pressure 28.5 in. Hg vapor pressure of water at $0.1^\circ C$ 4.6 torr (a) Find the volume of wet, cold air. (b) Convert the barometric pressure from inches of Hg to torr (c) Calculate the pressure of dry, cold air.

Transcript

00:01 Okay, so here a student is trying to determine the average molecular weight of the gas.

00:06 So here we know that the temperature is 22 .4 degrees celsius, and we know that atmospheric pressure is 751 millimeters of mercury, and we're assuming that the vapor pressure of water is 21 .1 millimeters of mercury.

00:29 So what we want to do is we want to find, first we want to find the pressure of just the gas, because we're trying to find the thing that we're calculating is about the gas specifically.

00:39 So then we need the pressure in relation to the gas.

00:42 But we know that the pressure, atmospheric pressure is going to be the sum of both the pressure of the water and the pressure of the gas inside the vurette.

00:55 And so it'll be 751 is equal to 21 .1 plus.

01:01 The pressure of the gas and so we can solve for pressure of the gas through subtraction.

01:07 So 751 minus 21 .1 is 729 .9 millimeters of mercury.

01:19 Then we have some data on the mass and the volume collected.

01:32 So the mass of the gas we have 0 .1766 and the volume that ended up being collected was 34 .22 milliliters.

01:43 Then we had 0 .1821 and 35 .06 milliliters was collected.

01:51 And then finally we had 0 .1795 and 34 .71 milliliters was collected.

02:02 And so what we want to do is we want to calculate the molecular weight of the gas.

02:08 And if we think about the units of molecular weight, mw is molecular weight.

02:15 It's in grams per mole.

02:16 And so we have the mass of each of the samples, but we don't have the moles of the sample.

02:21 And so what we need to do is we need to find a way to calculate the number of moles of each of these samples in order to calculate the molecular weight.

02:29 And so the way that we can find the moles of gas is because we have all of these pieces of data, we have temperature, pressure, and volume.

02:40 We can use the ideal gas law.

02:43 So pv equals nrt is the gas law.

02:45 And what we're interested in solving for is moles.

02:48 So pv over our t is going to be what we're going to be using to calculate moles.

02:54 So in order to use this equation, we need to make sure everything's in the proper units.

02:58 So we need temperature in kelvin, which means we'll need to convert celsius into kelvin by adding 273.

03:08 So this comes out to 295 .4.

03:14 We know the pressure of the gas in millimeters of mercury, but this needs to be in atmospheres in order to use the ideal gas law.

03:22 So 760 millimeters of mercury are in one atmosphere...

Question

Please give Ace some feedback